This invention relates to the field of integrated circuits (ICs). More particularly, it relates to multi-chip modules and their fabrication.
Multi-chip modules are known within the semiconductor fabrication industry. In a multi-chip module, several semiconductor dies, each die consisting of active and passive components, are coupled together and incorporated into a single completed IC package. For purposes of this invention, any IC containing two or more separate semiconductor dies will be called a multi-chip module. Examples of known multi-chip modules include a first semiconductor die with digital circuitry coupled together with a semiconductor die having analog circuitry, the two dies together being mounted within a single IC package. Similarly, digital semiconductor memory dies can be coupled together in whatever multiple is practical (e.g. 2*64 Mbit) and placed within a single IC package to create a large multi-chip module memory that is larger than would be practical or economical to fashion on a single semiconductor die.
The multiple semiconductor dies that form the active circuitry of these multi-chip modules can be mounted next to one another in a single “layer” or they can be placed one atop another. The number of dies in either a horizontal layout multi-chip module or a vertical layout multi-chip module will be constrained by the difficulty of forming connections between the dies, the cost of forming a package around multiple dies, the availability of printed circuit board (“PCB”) realty to mount the finished module and other, similar issues.
In multi-chip modules where the semiconductor dies are mounted one atop another, it is often necessary to place a non-conductive spacer between the active dies, to prevent short-circuits between them and to enable interconnection to the substrates. These spacers are typically formed from an inert insulating material like pure silicon, glass or a non-conductive polymer. Vias are created in these spacers to permit interconnections between the active dies that comprise the multi-chip module.
Although these known multi-chip modules are adequate for their intended uses, the insertion of spacers merely for insulation between active dies is wasteful of the module's internal area.